1. Field of the Invention
The present invention relates to a non-contact IC (Integrated Circuit) card communication system, and particularly to a modulation, demodulation and an antenna coupling circuit used in a non-contact IC card reader/writer and to a method of supplying power to the IC card while transferring data.
2. Description of the Related Art
FIG. 14 shows the arrangement of the conventional IC card communication system described in Japanese Patent Publication No. 5-20798. In the figure, reference numeral 10 denotes an IC card of non-contact type, and 11 is a loop antenna for data transmission and reception, provided in the IC card 10. Indicated by 20 is a reader/writer for writing and reading out data to/from the IC card 10, and 21 is a loop antenna provided on the reader/writer 20.
Data is written to or read out of the IC card 10 based on the transmission of pulse signals between the loop antenna 11 of the IC card 10 and the loop antenna 21 of the reader/writer 20 as shown in the FIG. 14. The IC card 10 is supplied with power in the energy form of electromagnetic wave emitted by the reader/writer 20.
However, the transmission of such pulse signals in the space causes spurious sidebands to emerge and also increases artificial noises. In the spatial transmission path having frequency characteristics with delay, it is difficult to carry out the high-rate data transfer with high reliability. The power supply to the IC card 10 based on the transmission of a pulse signal is not efficient due to the spreading of the frequency spectrum.